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Computer Architecture & Operating System [O.S.]

Architecture :Architecture : Functions as performed by a Computer Functions as performed by a Computer System. System.

Organization :Organization : Hardware blocks of a Computer System Hardware blocks of a Computer System

that helps to implement the Architecture. that helps to implement the Architecture. - CPU. - CPU. - Memory ( Main & Secondary).- Memory ( Main & Secondary). - Input & Output Peripherals.- Input & Output Peripherals.

Operating SystemOperating System : A System Software that helps all : A System Software that helps all type of users to operate a computer System.type of users to operate a computer System.

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The Functions of a Computer It is a It is a general purposegeneral purpose, , user programmable,user programmable, [ [ A A

program :program : MeaningfulMeaningful Group of instructions written Group of instructions written in a in a specific languagespecific language aimed to do a aimed to do a specific taskspecific task.] .] electronic gadget capable of doing the following electronic gadget capable of doing the following tasks :tasks :

• Data Processing (Numeric & Non Numeric)Data Processing (Numeric & Non Numeric) with with high degree of accuracyhigh degree of accuracy at a at a pretty high speedpretty high speed..

• Storage Storage of huge amount of information of various of huge amount of information of various types {Text (types {Text (in various formatsin various formats) , Picture, Audio, ) , Picture, Audio, Video} with reasonably high access speed Video} with reasonably high access speed [[Information BankInformation Bank ].].

• Communication Gateway [ Link to the World]Communication Gateway [ Link to the World]..

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Computer Vs. Other Electronic Gadgets

• Full User programmabilityFull User programmability : : Under some support environment. Under some support environment. Like Like do not divide if the divisor is 0do not divide if the divisor is 0 can be achievedcan be achieved through through programmingprogramming in a computer but such a thing in a computer but such a thing cannot be achievedcannot be achieved in in a calculator /organizer. a calculator /organizer.

• Wide ConnectivityWide Connectivity OptionsOptions: : To other computers and various To other computers and various types of peripherals.types of peripherals.

• Ease of upgradeabilityEase of upgradeability: : By installing new packages , By installing new packages , connecting state of the art peripherals, enhancing memory etc.connecting state of the art peripherals, enhancing memory etc.

• Downward CompatibilityDownward Compatibility : : Even after several phases of up-Even after several phases of up-gradation, almost all computer systems do provide support for gradation, almost all computer systems do provide support for several old versions of Hardware as well as software . This enables several old versions of Hardware as well as software . This enables investments made at any stage of a computer system useful and investments made at any stage of a computer system useful and effective for many years to come.effective for many years to come.

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Data Processing Activity of any Typical Computer (achieved by

executing some program)• Numeric OperationsNumeric Operations involving manipulation of Integers and involving manipulation of Integers and

Floating Point Numbers that includes very large values too Floating Point Numbers that includes very large values too ((achieved throughachieved through Special Application Programs) .Special Application Programs) .

• Logical OperationsLogical Operations like like comparing comparing two items. two items.

33.Non Numeric Operations.Non Numeric Operations that includes among all things the following that includes among all things the following ::

3a) Arranging Data Items like preparation of merit list.3a) Arranging Data Items like preparation of merit list. 3b) Manipulating Pictures & Graphics. 3b) Manipulating Pictures & Graphics. 3c) Multimedia applications ( Audio, Video, Graphics, Video) 3c) Multimedia applications ( Audio, Video, Graphics, Video)

3d) Create, format, send & receive messages of various forms3d) Create, format, send & receive messages of various forms..

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The Building Blocks of any Computer System

The Central Processing Unit [ C.P.U.] The Central Processing Unit [ C.P.U.] performs processing & control.performs processing & control.

The Memory System ( The Memory System ( InternalInternal as well as as well as Peripheral DevicesPeripheral Devices ) ) the storage the storage repository.repository.

The various Input & Output The various Input & Output Peripheral Peripheral Devices.Devices.

The links/connections between these The links/connections between these ComponentsComponents [ [ The variousThe various Bus ]. Bus ].

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The Operating System

The Operating System is a Modular, The Operating System is a Modular, Expandable Program which is Expandable Program which is

pre-designed & storedpre-designed & stored in the Memory in the Memory System that , when executed by the CPU, System that , when executed by the CPU, makes all the components of a makes all the components of a Computer functionComputer function in unisonin unison as well asas well as enables enables real world users to interact with real world users to interact with the Computer Systemthe Computer System..

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The Memory System The Common Storage Repository

of any Computer System The The Memory SystemMemory System of any Computer acts as the Common Storage of any Computer acts as the Common Storage

repository for the following : repository for the following : The The Operating SystemOperating System includes various Drivers , includes various Drivers ,

Resource Managers, Command Interpreters & Graphic Resource Managers, Command Interpreters & Graphic User Interfaces (GUIs).User Interfaces (GUIs).

Other Other System ProgramsSystem Programs like like Translator ( Compiler, Translator ( Compiler, Assembler) , Linker, Loader, System Libraries.Assembler) , Linker, Loader, System Libraries.

Various Various Application Modules Application Modules like like MS-Office, Internet MS-Office, Internet Browsers.Browsers.

Data in various forms ( Data in various forms ( Text, Pictures, Images, Audio Text, Pictures, Images, Audio & Video)& Video)

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Computer Components- 1 The Central Processing Unit [C.P.U.]

Structure Outline Each & every computer MUST carry out some form of processing , hence it must Each & every computer MUST carry out some form of processing , hence it must

possess : possess : A Processing Element / Processing Unit / Processor {Arithmetic, Logical, A Processing Element / Processing Unit / Processor {Arithmetic, Logical,

Manipulation of Messages} [ Manipulation of Messages} [ The Arithmetic Logic Unit (ALU)The Arithmetic Logic Unit (ALU) ]. ]. Some form of electronic local storage / Some form of electronic local storage / RegistersRegisters [ Scratchpad ]. [ Scratchpad ]. The processing tools i.e. the instructions available for processing . These The processing tools i.e. the instructions available for processing . These

instructions constitute any program framed to accomplish any kind of instructions constitute any program framed to accomplish any kind of processing implemented through the processing implemented through the Control UnitControl Unit . .

Proper sequencing the processing steps / instructions as well as controlling Proper sequencing the processing steps / instructions as well as controlling the various components to achieve the desired result through the the various components to achieve the desired result through the Control Control Unit.Unit.

Interface to the other components of the Computer ( achieved through Interface to the other components of the Computer ( achieved through Registers & Control UnitRegisters & Control Unit ). ).

The above are closely linked together hence are all encapsulated into the The above are closely linked together hence are all encapsulated into the C.P.U. { Central Processing Unit}.C.P.U. { Central Processing Unit}.

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The Functions of the CPU

The The Central Processing Unit Central Processing Unit performs the following tasks by performs the following tasks by executing Instructions executing Instructions of of some specific Operating some specific Operating System Modules / System program System Modules / System program stored in the stored in the Memory SystemMemory System..

1) 1) ControllingControlling all all peripheral devicesperipheral devices. [ . [ Relevant Relevant Device Driver Device Driver Program(s)Program(s)].].

2) 2) Communicating Communicating with all types of with all types of Remote Devices.Remote Devices. [ Network Protocol Program (s) [ Network Protocol Program (s) acting onacting on Network Cards ] Network Cards ] 3) 3) RecognizingRecognizing user commands [ user commands [ Command Interpreters / Command Interpreters /

GUI (Graphic User Interface) ]. GUI (Graphic User Interface) ]. 4) 4) InputtingInputting Data [ Data [ Device Driver of the O.S.Device Driver of the O.S.].]. 5) Producing 5) Producing Output Output (on screen /or on printer) after obtaining (on screen /or on printer) after obtaining

Data from Main/Secondary Memory.[Device Driver of the Data from Main/Secondary Memory.[Device Driver of the O.S.]O.S.]

6) Performing 6) Performing arithmetic arithmetic & & logical logical operations.[ As per operations.[ As per Specified Instruction(s) of the executing program (s)]Specified Instruction(s) of the executing program (s)]

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The Components of the C.P.U. Arithmetic & Logical Processing Unit [ Arithmetic & Logical Processing Unit [ The A.L.UThe A.L.U ].].

Associated Data Storage Components / Scratch Pad Storage. Associated Data Storage Components / Scratch Pad Storage. Electronic Storage (Electronic Storage (The RegistersThe Registers).).

The implementation of the The implementation of the Instruction SetInstruction Set as well as the unit that as well as the unit that controls & sequencescontrols & sequences all operations in accordance with the supported all operations in accordance with the supported Instruction Set [ Instruction Set [ The Control UnitThe Control Unit ] . ] .

The The interfaceinterface with other components of a Computer [Special with other components of a Computer [Special Purpose Registers along with associated controls ].Purpose Registers along with associated controls ].

( All will be illustrated in due course ).( All will be illustrated in due course ).

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The Components of the CPU

Control Unit

ALUStorage & Interface Registers

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The CPU Performance Parameters - 1

N.B: N.B: All the activities of any Computer System are being carried out by the CPU by All the activities of any Computer System are being carried out by the CPU by executingexecuting some some machine level /low level instruction.machine level /low level instruction.

1. 1. CPU Speed :CPU Speed : Each Each machine instructionmachine instruction takes a takes a definite timedefinite time to complete execution. to complete execution. This time is measured in terms of the This time is measured in terms of the Number of CPU Clock Periods needed to Number of CPU Clock Periods needed to execute that instruction execute that instruction ( The Instruction Latency).( The Instruction Latency).

Hence one way to measure the CPU speed is Hence one way to measure the CPU speed is Number of Instructions executed / Number of Instructions executed / second (second (termed as thetermed as the Throughput) . Throughput) .

Typical unit isTypical unit is MIPS (MIPS (Millions of Instructions per secondMillions of Instructions per second) or MFLOPS () or MFLOPS (Millions of Millions of Floating point Operations performed per second.)Floating point Operations performed per second.)

However one normally finds the However one normally finds the CPU Clock frequencyCPU Clock frequency as as rough estimaterough estimate of its of its speed i.e. speed i.e. higher the clock frequency higher will be the CPU speedhigher the clock frequency higher will be the CPU speed. .

But in actual terms speed will be affected depending on the most frequently used But in actual terms speed will be affected depending on the most frequently used instructions hence instructions hence thethe Throughput Throughput happens to be a more fair estimate of the CPU happens to be a more fair estimate of the CPU speed speed estimated by executingestimated by executing some some benchmark programs .benchmark programs .

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The CPU Performance Parameters - 2

2. 2. CPU Processing Power :CPU Processing Power : The The Operand Size (in bits)Operand Size (in bits) it can handle at it can handle at one go i.e. one go i.e. in a single machine instruction normallyin a single machine instruction normally. This is directly . This is directly related to itsrelated to its ALU ( A ALU ( Arithmeticrithmetic L Logicogic U Unitnit a purely combinational a purely combinational Circuit) Circuit) widthwidth..

e.g. e.g. Pentium is a 32 Bit CPUPentium is a 32 Bit CPU Any Machine level instruction of a Any Machine level instruction of a Pentium Processor can handle 32 bit operands or Pentium contains Pentium Processor can handle 32 bit operands or Pentium contains 32 bit Integer ALUs32 bit Integer ALUs. .

N.B:N.B: This Operand Sized based classification is interesting in the sense This Operand Sized based classification is interesting in the sense that any that any n bit CPUn bit CPU can also be used to handle larger sized data can also be used to handle larger sized data provided one writes proper programs to achieve that provided one writes proper programs to achieve that which gets which gets translated into n bit processing instructionstranslated into n bit processing instructions by the by the Translator Translator ProgramProgram ( (The CompilerThe Compiler).).

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Computer Components – 2 [ The Memory ] Memory : Essential to create any form of Memory : Essential to create any form of

Information Bank/ Information Bank/ Common Storage Common Storage Repository ( as illustrated earlier). Repository ( as illustrated earlier).

Wide range & types of Memory & Storage Wide range & types of Memory & Storage Media are available/ in use now –a –days . Media are available/ in use now –a –days .

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Generalized Memory Structure

Large Data Storage repository.Large Data Storage repository. Structure is NOT dictated by what is stored in that Structure is NOT dictated by what is stored in that

memory (memory (Content IndependentContent Independent).). Several access mechanism modes exists to access Several access mechanism modes exists to access

it’s content . it’s content . Any memory can be thought to be composed of Any memory can be thought to be composed of

several several individuallyindividually addressable blocksaddressable blocks each of each of which contains some which contains some datadata ( (generic termgeneric term) item. ) item.

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User Requirement/ Ideal View point of the Computer Memory

Should be Infinite Sized.Should be Infinite Sized. Should possess High Speed of access.Should possess High Speed of access. Should be of Low Cost .Should be of Low Cost . Has to be Reliable.Has to be Reliable. Must be Expandable with little or no affect on Must be Expandable with little or no affect on

the existing system configuration.the existing system configuration. Must be Must be flexibleflexible & & adaptableadaptable to change in size to change in size

as well as to compatibility with new emerging as well as to compatibility with new emerging technologies.technologies.

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Classification of Memory Classification A Classification A ( ( Media TypesMedia Types).). ElectronicElectronic [ ROM, EPROM, Static RAM, Dynamic RAM, Flash , Memory Stick]. [ ROM, EPROM, Static RAM, Dynamic RAM, Flash , Memory Stick]. MagneticMagnetic [ Hard Disk, Flex Disk, Tape, DAT]. [ Hard Disk, Flex Disk, Tape, DAT]. Optical Optical [CD-R/ -RW, DVD-R/RW, DVD-RAM, Blue-Ray DVD, HD DVD].[CD-R/ -RW, DVD-R/RW, DVD-RAM, Blue-Ray DVD, HD DVD].

Classification B Classification B ( ( Data Retention PropertyData Retention Property).). Volatile.Volatile. [ Electronic ] [ Electronic ] Non VolatileNon Volatile. [ Flash, Magnetic , Optical].. [ Flash, Magnetic , Optical].

Classification C Classification C ( ( Alterability PropertyAlterability Property).). User AlterableUser Alterable.[ RAM, Flash, Disk, Tape, DAT, CD-RW, Blue-Ray / HD / Ordinary DVD-RW].[ RAM, Flash, Disk, Tape, DAT, CD-RW, Blue-Ray / HD / Ordinary DVD-RW] Non Alterable [ROM, EPROM, Flash, CD, DVD]Non Alterable [ROM, EPROM, Flash, CD, DVD]..

Classification D Classification D ( CPU Proximity & Accessibility, ( CPU Proximity & Accessibility, Most System RelevantMost System Relevant).). Register.Register. {Electronic, Volatile, User Alterable}. {Electronic, Volatile, User Alterable}. Cache. {Cache. {Electronic, Volatile, Transparent to User}Electronic, Volatile, Transparent to User} Main / PrimaryMain / Primary. {Electronic, Volatile, User Alterable}.. {Electronic, Volatile, User Alterable}. Secondary ( Secondary ( Some ExternalSome External ) ) . {Flash, Magnetic Disks & Tapes, Optical, Non Volatile, . {Flash, Magnetic Disks & Tapes, Optical, Non Volatile,

Some User Alterable}.Some User Alterable}.

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Peripheral & Remote Devices

Peripherals/ Peripheral DevicesPeripherals/ Peripheral Devices : All those Devices that : All those Devices that lie in the lie in the Periphery Periphery of the CPU. All Peripheral Devices are of the CPU. All Peripheral Devices are connected to the CPU through several Buses (as illustrated connected to the CPU through several Buses (as illustrated earlier) and are controlled by the CPU through some earlier) and are controlled by the CPU through some Device Driver program (s) Device Driver program (s) [ part of the Operating [ part of the Operating System]System]..

Remote Devices :Remote Devices : Those which are far away from the current Those which are far away from the current CPU/ Computer System connected through the Network CPU/ Computer System connected through the Network Interface.Interface.

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Input Output Peripherals

Helps to establish link between computer / Helps to establish link between computer / cyber world & Real World. Various forms cyber world & Real World. Various forms of I/O Peripherals exists.of I/O Peripherals exists.

Common Input PeripheralsCommon Input Peripherals : Key : Key board, Mouse.board, Mouse.

Common Output PeripheralsCommon Output Peripherals : Video : Video Monitor, Printer.Monitor, Printer.

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Input Peripheral Devices and their Functions ( Architectural

Aspects) These are employed to feed data , program, picture, These are employed to feed data , program, picture,

commands to the Computer System. A few commonly commands to the Computer System. A few commonly used devices are the following :used devices are the following :

• Keyboard ( Keyboard ( The earliest and still most commonly used The earliest and still most commonly used Input Device).Input Device).:: To type in Commands and/or Data To type in Commands and/or Data [Alphabets, Digits, Symbols etc.][Alphabets, Digits, Symbols etc.]

• The Mouse :The Mouse : Commands are given by clicking its Commands are given by clicking its left/right button. It works in a Graphic Environment left/right button. It works in a Graphic Environment where user is given option to select among several where user is given option to select among several Options in a menu by moving mouse button on to that Options in a menu by moving mouse button on to that item and clicking on thatitem and clicking on that..

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Output Peripherals and their Functions- 1

Output Peripherals are responsible for providing some Output Peripherals are responsible for providing some form of response/result to the user. Commonly used form of response/result to the user. Commonly used Output peripheral devices are :Output peripheral devices are :

• Visual Display Unit (VDU) Screen / MonitorVisual Display Unit (VDU) Screen / Monitor : Is used : Is used to display the following to display the following

Anything typed in via keyboard.Anything typed in via keyboard. The various menus available to the user.The various menus available to the user. The response generated by the system to various user The response generated by the system to various user

commands in some way. commands in some way. The result generated by running various programs/ The result generated by running various programs/

packages.packages.

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Output Peripherals and their Functions - 2

2. 2. Printers :Printers : Used to produce printed Outputs / Hard Copy. Various types Used to produce printed Outputs / Hard Copy. Various types of printers :of printers :

Impact PrintersImpact Printers : Where there exists a physical printing Mechanism/ : Where there exists a physical printing Mechanism/ print headprint head that strikes on the paper & ink ribbon to make an impression that strikes on the paper & ink ribbon to make an impression on the Paper. These mostly print in Black . Examples of such printers are on the Paper. These mostly print in Black . Examples of such printers are Dot Matrix , Line , Band etc.Dot Matrix , Line , Band etc.

Non Impact Printers :Non Impact Printers : Here there exists no physical printing heads Here there exists no physical printing heads rather printing is done by electronic/electrostatic mechanism that regulate rather printing is done by electronic/electrostatic mechanism that regulate the flow of ink/toner which are electro statically deposited on the paper. the flow of ink/toner which are electro statically deposited on the paper. These can print both in Monochrome (black) as well as in Color. These can print both in Monochrome (black) as well as in Color. Commonly used printers are Inkjet, Desk jet, Laser etc.Commonly used printers are Inkjet, Desk jet, Laser etc.

Graphic PrintersGraphic Printers like like Dot Matrix, Inkjet, Desk Jet, LaserDot Matrix, Inkjet, Desk Jet, Laser can print can print both both text text as well as as well as pictures pictures while while Line Printer, Band PrinterLine Printer, Band Printer can only print can only print characters . But these are high speed & rugged compared to graphic characters . But these are high speed & rugged compared to graphic printers . printers .

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Peripheral Interfaces - 1 Most of the peripheral devices helps in establishing human interface to the computer Most of the peripheral devices helps in establishing human interface to the computer

System (mainly CPU & Memory).System (mainly CPU & Memory).

Each of the peripheral differs in characteristics from each other as well as from the Each of the peripheral differs in characteristics from each other as well as from the electronic parts (CPU & Memory) in terms of electrical features and operating speed. electronic parts (CPU & Memory) in terms of electrical features and operating speed.

Some kind of programs are required to control all the various peripherals (Some kind of programs are required to control all the various peripherals (Device Device DriversDrivers) .) .

Users interact with any computer either by some command or alternately by mouse click Users interact with any computer either by some command or alternately by mouse click . Hence some form of command interpreter or Graphic User interface [GUI] is needed .. Hence some form of command interpreter or Graphic User interface [GUI] is needed .

These device driver programs as well as Command Interpreter & GUI forms part of the These device driver programs as well as Command Interpreter & GUI forms part of the existing Operating System .existing Operating System .

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Peripheral Interfaces - 2

All peripherals must possess the following things :All peripherals must possess the following things :

a) An Electronic a) An Electronic Peripheral Interface Peripheral Interface that helps to that helps to isolate the CPU & Main Memory from the diverse world isolate the CPU & Main Memory from the diverse world of peripherals.of peripherals.

b) CPU – Peripheral connectivity is established through b) CPU – Peripheral connectivity is established through the following components :the following components :

1) Electronically addressable Command Register (Write Only).1) Electronically addressable Command Register (Write Only).

2) Electronically addressable Status Register (Read Only).2) Electronically addressable Status Register (Read Only). 3) Electronically addressable Local Data Buffer (Read/Write).3) Electronically addressable Local Data Buffer (Read/Write).

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BUS : The Connection Gateway

Group of Electrical Lines ( cables and/or Group of Electrical Lines ( cables and/or PCB Tracks OR both ) performs a PCB Tracks OR both ) performs a particular task in particular task in unition.unition.

Helps to connect the Different Components Helps to connect the Different Components of any Computer System.of any Computer System.

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CPU – External World Connectivity - 1

1) CPU must be able to address each device interface 1) CPU must be able to address each device interface as well as each memory location. This Address is sent as well as each memory location. This Address is sent via a group of electrical lines / via a group of electrical lines / PCB TracksPCB Tracks termed as the termed as the Address busAddress bus..

2) CPU sends / receives 2) CPU sends / receives datadata to / fromto / from the device the device interface & memory through a separate group of lines interface & memory through a separate group of lines termed as termed as Data BusData Bus..

3) CPU 3) CPU sendssends CommandCommand to / or to / or readsreads Device Device StatusStatus from the device interface / memory via a 3 from the device interface / memory via a 3rdrd group of group of lines known as the lines known as the Control BusControl Bus..

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The Different BusesAddress BusAddress Bus - - Group of lines that is used to carry address Group of lines that is used to carry address

information from the CPU to the concerned device(s). information from the CPU to the concerned device(s). Address is one that helps the CPU to select one among Address is one that helps the CPU to select one among many devices. Hence it is many devices. Hence it is unidirectionalunidirectional..

Data BusData Bus - The group of lines used to carry data/information from the - The group of lines used to carry data/information from the device to CPU &device to CPU & vice versa. It is always vice versa. It is always bi-directionalbi-directional..

Control BusControl Bus – The group of lines that enables the CPU to control various – The group of lines that enables the CPU to control various activities by activities by sendingsending appropriate commandsappropriate commands as well as as well as monitor statusmonitor status of of the concerned device e.g. the concerned device e.g. Read SignalRead Signal, , Write Signal,Write Signal, Status Set SignalStatus Set Signal. .

Each bus consists of a number of lines, which is represented in a compact Each bus consists of a number of lines, which is represented in a compact manner.manner.

Bi Directional Bus composed of 32 Lines32

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Memory Bus & I/O Bus As has already been mentioned , Peripherals presents a much larger diverse As has already been mentioned , Peripherals presents a much larger diverse

interface scenario than the Memory.interface scenario than the Memory.

The entire Memory hierarchy interacts with the CPU through some pre-The entire Memory hierarchy interacts with the CPU through some pre-specified protocol. specified protocol.

Whereas, large diverse nature of Peripheral Interfaces demands a much larger Whereas, large diverse nature of Peripheral Interfaces demands a much larger variety of interface protocols . variety of interface protocols .

This demands different set of Buses , namely, I/O Bus and Memory Bus to This demands different set of Buses , namely, I/O Bus and Memory Bus to connect peripherals and Memory respectively with the CPU. connect peripherals and Memory respectively with the CPU.

However, any type of BUS, in principle , must essentially compose of However, any type of BUS, in principle , must essentially compose of ADDRESS, DATA & CONTROL Buses only differing in signal level & ADDRESS, DATA & CONTROL Buses only differing in signal level & layout.layout.

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Oversimplified Bus Level Organization